CN1329360C - Preparation of substituted phthalic anhydride, especially 4-chlorophthalic anhydride - Google Patents

Abstract

The present invention relates to a synthesis method of substituted phthalic anhydride (IV) which has the chemical formula disclosed in the specification, wherein R represents halogen, and comprises an aromatic or aliphatic group containing 1 to 18 carbon atoms, hydrogen or nitryl. The method is imide exchange reaction between substituted N-alkyl phthalimide (V) and substituted tetrahydrophthalic anhydride (VI), wherein R represents alkyl containing 1 to 18 carbon atoms. Substituted N-alkyl tetrahydrophthalimide (VII) as a byproduct of the reaction can be converted into the substituted N-alkyl phthalimide (V) by aromatization.

Description

Preparation of substituted phthalic anhydrides

Cross References to Related Applications

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Statement Regarding Federally Funded Research and Development

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Background of the invention

The present invention relates to the preparation method of acid anhydride. More specifically, the present invention relates to a transimidation-based process for the preparation of anhydrides.

Polyetherimide is a high heat-resistant engineering plastic with many uses. As disclosed in U.S. Patent No. 5,229,482, a route for the synthesis of polyetherimides proceeds via bis(4-chlorophthalimide) having the structure (I)

wherein X is a divalent alkylene, cycloalkylene or arylene moiety. Bis(4-chlorophthalimide) (II) wherein X is 1,3-phenyl is particularly useful.

Typically, bis(chlorophthalimide) (I) and (II ).

4-Chlorophthalic anhydride is an expensive raw material, which currently has to be synthesized on commission. Existing routes for the synthesis of 4-chlorophthalic anhydride result in a mixture of isomers that are difficult to separate or limited by being expensive. For example, the Diels-Alder condensation reaction of maleic anhydride with 2-chloro-1,3-butadiene to form 4-chlorotetrahydrophthalic anhydride followed by aromatization in the presence of bromine requires subsequent recovery of HBr. Attempted thermal aromatization of 4-chloro-tetrahydrophthalic anhydride resulted in low yields of 4-chlorophthalic anhydride and formation of tars. This route and others are disclosed in US Patent Nos. 5,059,697, 5,003,088, 5,322,954, 4,978,760 and 5,233,054.

Contents of the invention

A new method for the synthesis of phthalic anhydride (IV) is an imide exchange reaction between the corresponding N-alkylphthalimide (V) and tetrahydrophthalic anhydride (VI) ,

wherein R' is halogen, an aromatic group containing 6 to about 18 carbon atoms, an aliphatic group containing 1 to about 18 carbon atoms, hydrogen or nitro,

wherein R' in formula (IV) is the same as R' in formula (V), and wherein R is an alkyl group having 1 to about 18 carbon atoms,

The by-product of the imide exchange reaction is N-alkyltetrahydrophthalimide (VII)

In an advantageous feature of the process, wherein R' in formulas (V), (VI) and (VII) are identical, the Aromatization to prepare the corresponding N-alkylphthalimide (V).

Detailed ways

A convenient method for the formation of phthalic anhydride (IV) is by imide exchange between the corresponding N-alkylphthalimide (V) and tetrahydrophthalic anhydride (VI) reaction. A by-product of this reaction is N-alkyltetrahydrophthalimide (VII). The by-products are preferably converted to give the corresponding N-alkylphthalimides (V).

The structure of the product phthalic anhydride (IV) is

wherein R' is halogen, an aromatic or aliphatic group containing 1 to about 18 carbon atoms, hydrogen or nitro. The structure of the starting N-alkylphthalimide (V) is

wherein R' is as described above, and R is a straight chain or branched alkyl group having 1 to about 18 carbon atoms, such as methyl, ethyl, propyl, and the like. N-Alkylphthalimides (V) can be obtained by aromatization of the corresponding N-alkyltetrahydrophthalimides. Aromatization can be achieved by any method known in the art, such as those taught in US Patent Nos. 5,233,054, 5,003,088, 5,059,697 and 4,978,760. Aromatization can also be achieved by passing the N-alkyltetrahydrophthalimide over a transition metal catalyst such as _V2O5 at _a temperature of about 250°C to about 270°C. Alternatively, N-alkylphthalimides can be obtained by heating tetrahydrophthalic anhydride and the desired alkyl or aromatic amine at a temperature of from about 50°C to about 250°C for up to about 5 hours ( V). The resulting product N-alkylphthalimide can be isolated by any method known in the art such as distillation or column chromatography. The N-alkylphthalimide is preferably N-alkyl 4-chlorophthalimide.

Tetrahydrophthalic anhydride (VI) can be obtained by the Diels-Alder condensation reaction of the dienophile maleic anhydride and a diene substituted by R', wherein R' is as defined above. The conditions for this reaction are known in the chemical literature. Suitable R' substituents include, but are not limited to, halogen, aromatic or aliphatic groups containing 1 to about 18 carbon atoms, hydrogen or nitro. A preferred diene is 2-chloro-1,3-butadiene (chloroprene).

The advantageous feature of the method is that when R' in (V) and (VI) is the same, the by-product N-alkyltetrahydrophthalimide (VII) of the imide exchange reaction can be Transformation is carried out to prepare N-alkylphthalimides (V), as described above. Due to this advantageous feature, it is expected that the synthesis of 4-chlorophthalic anhydride can be carried out in batch or continuous mode.

As shown in Scheme 1, the method is particularly useful for the formation of 4-chlorophthalic anhydride (III), an important intermediate in the synthesis of polyetherimides.

Thus, 4-chlorophthalic anhydride was prepared by the imide exchange reaction of N-methyl-4-chlorophthalimide (VIII) and 4-chlorotetrahydrophthalic anhydride (IX) (III). The by-product N-methyl-4-chlorotetrahydrophthalimide (X) of the imide exchange reaction is preferably converted to N-methyl-4-chlorophthalimide by aromatization Imine (VIII).

All patents cited herein are hereby incorporated by reference.

The invention is further described by the following non-limiting examples.

Example

Example 1. Synthesis of N-methyl-4-chlorophthalimide (VIII)

Charge 186.5 g (1 mole) of 4-chlorotetrahydrophthalic anhydride into a suitably configured glass reaction vessel and heat to 150° C. under nitrogen protection. Methylamine gas (32 grams, 1.03 moles) was then introduced subsurface of the reaction vessel for 30 minutes. The reaction mixture was then heated at 180° C. for 3 hours. The product was then distilled to give N-methyl-4-chlorophthalimide in about 95% yield.

Example 2. Synthesis of 4-chlorotetrahydrophthalic anhydride (IX)

156.9 g (1.6 moles) of maleic anhydride and 250 ml of toluene were added to the flask. 25 ml of toluene was removed by distillation to dry the solution. 150 g (1.69 moles) of chloroprene dissolved in 250 ml of xylene was slowly added to the flask. The total addition took 30 minutes. The resulting solution was then heated at 55°C for 3 hours. The solution was then distilled to remove the solvent. The remaining material was distilled at 160-165° C. (1-2 mm pressure) to obtain 4-chlorotetrahydrophthalic anhydride (253 g) with a yield of 85%.

Example 3. Synthesis of 4-chlorophthalic anhydride (III)

Add 1.5g of 4-chlorotetrahydrophthalic anhydride, 0.262g of N-methyl-4-chlorophthalimide, 0.841g of triethylamine and 20ml of water into a 50ml resealable stainless steel tube. The tube was sealed and heated in an oil bath at 170°C for 3 hours, then cooled to room temperature.

A small sample in the aqueous phase was analyzed by means of GCMS. The analysis revealed that 83.2% of the exchanges took place. Analysis also showed that the reaction mixture consisted of 2.4 mol% N-methyl-4-chlorophthalimide, 11.9 mol% N-methyl-4-chlorotetrahydrophthalimide, 11.9 mol % of 4-chlorophthalic anhydride (as the triethylamine salt of the corresponding diacid) and 73.8 mol % of 4-chlorotetrahydrophthalic anhydride (as the triethylamine salt of the corresponding diacid).

The aqueous phase was extracted with 20 ml of toluene containing 3 wt% triethylamine in a separatory funnel at room temperature. The toluene extraction effectively removed N-methyl-4-chlorotetrahydrophthalimide and unreacted N-methyl-4-chlorophthalimide in the aqueous phase. The aqueous phase also contained 4-chlorophthalic anhydride (as the triethylamine salt of the corresponding diacid) and 4-chlorotetrahydrophthalic anhydride (as the triethylamine salt of the corresponding diacid). The aqueous phase is distilled, during which the triethylamine salt decomposes to release water and triethylamine with simultaneous formation of 4-chlorophthalic anhydride and 4-chlorotetrahydrophthalic anhydride. Water and triethylamine are taken overhead, while the bottoms are collected. The bottoms are then distilled in order to separate 4-chlorotetrahydrophthalic anhydride from 4-chlorophthalic anhydride A. 4-Chlorotetrahydrophthalic anhydride was remixed with previously collected water and triethylamine (TEA) and reused.

Example 4. Conversion of N-methyl-4-chlorotetrahydrophthalimide (X) to N-methyl-4-chlorophthalimide

The gas phase _reaction was carried out in a heat pipe reactor packed with about 13 g of _V2O5 containing catalyst. The inlet of the heat pipe reactor was connected to a flow controller and a heated syringe pump. The flow controller controls the flow of purified air. A heated syringe pump contained 4-chloro-N-methyltetrahydrophthalimide and delivered it to the heat pipe reactor at a constant rate of 0.05 milliliters per minute. The outlet of the heat pipe reactor was connected to a receiver cooled in an ice bath, where the reaction product was collected. The heat pipe reactor was maintained at 260 °C. The reaction products were then analyzed by gas chromatographic techniques after the system equilibrated for 10-20 minutes. At a flow rate of 90 ml/min, all of the N-methyl-4-chlorotetrahydrophthalimide was converted to N-methyl-4-chlorophthalimide.

While a preferred embodiment has been shown and described, various modifications and substitutions can be made therein without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.

Claims (5)

1. method that is used to prepare Tetra hydro Phthalic anhydride, it comprises:

The Tetra Hydro Phthalic Anhydride (VI) that makes N-alkyl phthalic imide (V) and replace carries out the imide permutoid reaction,

Wherein R ' is selected from halogen, comprises the aromatic group of 6～18 carbon atoms, the aliphatic group that comprises 1～18 carbon atom, hydrogen and nitro, and R is the alkyl with 1～18 carbon atom,

Wherein R ' is selected from halogen, comprises the aromatic group of 6～18 carbon atoms, the aliphatic group that comprises 1～18 carbon atom, hydrogen and nitro,

Wherein (V) is identical with R ' in (VI),

To produce N-alkyl tetrahydro phthalic imidine (VII) and the Tetra hydro Phthalic anhydride (IV) that replaces:

2. the process of claim 1 wherein that Tetra hydro Phthalic anhydride is the 4-chloro-phthalic anhydride, the N-alkyl phthalic imide is N-alkyl-4-chlorophthalimide.

3. the method for claim 1, it also comprises by aromizing N-alkyl tetrahydro phthalic imidine is converted into the corresponding N-alkyl phthalic imidine.

4. the method for claim 3 wherein is converted into the corresponding N-alkyl phthalic imidine with N-alkyl tetrahydro phthalic imidine in the presence of vanadium oxide.

5. the process of claim 1 wherein that N-alkyl tetrahydro phthalic imidine (VII) is N-methyl-4-chlorine tetrahydric phthalimide.